Since the beginning of global warming concerns, chlorofluorocarbon manufacturers have had to produce compounds that perform substantially the same as fully halogenated chlorofluorocarbons without the adverse environmental impact. Only through the introduction of these new compounds have their environmental impact been completely understood. In certain instances, some of these new compounds have been removed from the marketplace. These types of issues make the flooding agent, extinguishant, propellant and refrigerant production industry a dynamic and ever-changing marketplace where processes for the production of chlorofluorocarbons and fluorocarbons are advancing quickly to accommodate both environmental as well as economical requirements.
Some useful compounds in this area include both saturated and unsaturated fluorocarbons, such as 1,1,1,2,3,3,3-heptafluoropropane (CF3—CFH—CF3, HFC-227ea), 1,1,1,2,2,3,3-heptafluoropropane (CF3—CF2—CHF2, HFC-227ca) and hexafluoropropene (hexafluoropropylene, HFP, CF3—CF═CF2, FC-1216). One well known method of synthesizing these compounds begins with the chlorofluorination of propane, propylene or partially halogenated C-3 hydrocarbons with hydrogen fluoride (HF) and chlorine (Cl2) in the presence of a metal-containing solid catalyst. Examples of this chlorofluorination step can be found in U.S. Pat. Nos. 5,057,634 and 5,043,491 to Webster. As taught by Webster, the chlorofluorination step produces a number of saturated perhalogenated chlorofluorocarbons, including: (A) C3Cl5F3; (B) C3Cl4F4; (C) C3Cl3F5; (D) 1,2-dichlorohexafluoropropane (CF3—CClF—CClF2, CFC-216ba); (E) 2,2-dichlorohexafluoropropane (CF3—CCl2—CF3, CFC-216aa); (F) 1-chloroheptafluoropropane (CF3CF2CClF2, CFC-217ca); (G) 2-chloroheptafluoropropane (CF3CClFCF3, CFC-217ba); and (H) octafluoropropane (CF3—CF2—CF3, FC-218). While the FC-218 is useful and can be separated from other perhalogenated reaction products, it is not an efficient or economical intermediate in the synthesis of HFC-227ea, HFC-227ca or FC-1216. As indicated in the '491 patent, the predominant reaction products resulting from the chlorofluorination of propane with HF and Cl2 is CFC-216aa, which is fluorinated and then dehalogenated to hexafluoropropene (FC-1216).
Due primarily to environmental as well as toxicological concerns, demand is increasing for isomerically pure chlorofluorocarbons and hydrofluorocarbons. Teachings such as those described above cannot begin to address these issues and concerns because efficiency of production as well as isomeric purity were not contemplated. Prior art of similar chemistry does not allow for the exclusive production of the HFC-227ea, but only as a mixture or by-product with FC-1216. The unsuitability of FC-1216 for a fire suppressant does not make this a viable or efficient route.
A need exists to develop a method of chlorofluorinating inexpensive C-3 reactants that eliminates one or more by products of chlorofluorination, particularly FC-218 and undesired isomers which cannot be recycled to produce HFC-227ea or HFC-227ca. Moreover, a long felt need exists for extending the lifetime of catalysts used in these reactions.
Furthermore, the reaction products generated from these steps require purification. U.S. Pat. Nos. 6,018,083 to Manogue and 6,211,135 to Miller respectively teach the partial separation (azeotropes) of chlorofluorocarbons C3ClF7 (CFC-217) and C3Cl2F6 (CFC-216) from HF. These references demonstrate the practical difficulty of separating reaction product mixtures with conventional distillation techniques. The formation of azeotropes requires the use of subsequent or expensive distillation techniques to produce a pure product that can be used as a final product or as an intermediate reactant. A need remains for processes that separate chlorofluorination reaction products without forming azeotropes.
The present invention provides processes for the chlorofluorination of aliphatic, olefinic or partially halogenated hydrocarbons in the presence of a catalyst that results in the substantial elimination of FC-218 as a by-product in the chlorofluorination reaction and that efficiently converts the starting material to the desired isomer. The present invention also provides processes for the efficient purification of reaction product streams.